Update XRInputSource and implement originOffset for XRReferenceSpace.

To match the latest WebXR spec, remove XRInputPose and no longer expose XRFrame.getInputPose to JS.
The logic from getInputPose has been moved to the private methods XRFrame.GetGripPose and XRFrame.GetTargetRayPose, which are called from XRFrame.getPose.

Also take changes to originOffset into account when quering viewer pose and input (ray and grip) poses for a frame.
This is required by the spec and enables teleportation behavior in VR space.
The input selection webxr test page has changes that klausw@ made to test this use case for both 3DoF and 6DoF headsets.

Bug: 922204, 922166
Change-Id: I608e528151a5a29d51a29f17540a062236e7b1f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1502072
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Reviewed-by: Klaus Weidner <klausw@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#640524}
26 files changed